Commentary on the Bible, by Adam Clarke, , at sacred-texts.com
The psalmist begs God to take his part against his enemies, Psa 43:1, Psa 43:2; to send his light and truth to guide him to the tabernacle, Psa 43:3; promises, if brought thither, to be faithful in the Divine service, Psa 43:4; chides himself for despondency, and takes courage, Psa 43:5.
There is no title to this Psalm in the Hebrew, nor in the Chaldee. The Syriac says it was composed "by David when Jonathan told him that Saul intended to slay him." The Arabic says of this, as of the preceding, that it is a prayer for the backsliding Jews. It is most evidently on the same subject with the forty-second Psalm, had the same author or authors, and contains the remaining part of the complaint of the captive Jews in Babylon. It is written as a part of the forty-second Psalm in forty-six of Kennicott's and De Rossi's MSS.
Judge me, O God, and plead my cause - ריבה ריבי ribah ribi, a forensic term, properly enough translated, plead my cause, be my counsellor and advocate.
Ungodly nation - The Babylonians; the impious, perfidious, wicked, and deceitful Babylonians.
The deceitful and unjust man - Nebuchadnezzar.
For those art the God of my strength - The psalmist speaks here, as in other places in the person of the whole Israelitish people then captive in Babylon. We still acknowledge thee for our God. Why are we cast off? Now that we are humbled and penitent, why are we not enlarged? Why are we not saved from this oppression of the Babylonians?
O send out thy light and thy truth - We are in darkness and distress, O send light and prosperity; we look for the fulfillment of thy promises, O send forth thy truth. Let thy fight guide me to thy holy hill, to the country of my fathers; let thy truth lead me to thy tabernacles, there to worship thee in spirit and in truth.
Then will I go unto the altar - When thy light - a favorable turn on our affairs, leads us to the land of our fathers, and thy truth - the fulfillment of thy gracious promises, has placed us again at the door of thy tabernacles, then will we go to thy altar and joyfully offer those sacrifices and offerings which thy law requires, and rejoice in thee with exceeding great joy.
Why art thou cast down - Though our deliverance be delayed, God has not forgotten to be gracious. The vision, the prophetic declaration relative to our captivity, was for an appointed time. Though it appear to tarry, we must wait for it. In the end it will come, and will not tarry; why then should we be discouraged? Let us still continue to trust in God, for we shall yet praise him for the fullest proofs of his approbation in a great outpouring of his benedictions.